This section provides background information related to the present disclosure which is not necessarily prior art.
Automobiles, trucks, buses and other vehicles are commonly designed using independent front and/or rear suspension systems to connect unsprung components of the vehicle, such as the wheels and brakes, to the chassis of the vehicle. Independent suspension systems normally include an upper control arm, a lower control arm, and a hub or knuckle that supports one of the wheels. Each control arm is attached to a frame or other support structure of the vehicle using one or more bushing assemblies. The bushing assemblies decouple torsional input from other articulation directions. Each bushing assembly typically consists of an outer metal sleeve that is pressed into the control arm, an elastomeric bushing positioned within the outer metal sleeve, a thrust bearing that extends through the center of the elastomeric bushing, and an inner metal sleeve that extends through the center of the thrust bearing. The inner metal sleeve is connected to a bracket on the frame or other support structure of the vehicle. In some examples, a bolt extends through the inner metal sleeve and secures the control arm and the bushing assembly to the frame by mating with an appropriate bracket. As the vehicle travels, relative movement between the chassis and the unsprung components of the vehicle is accommodated by flexing of a coil spring, a torsion bar, an air spring, or by another resilient device. The flexing of the resilient device causes the ends of the control arms to pivot on the bushing assemblies.
The thrust bearing facilitates the pivotal motion of the inner metal sleeve relative to the outer metal sleeve and the elastomeric bushing. The elastomeric bushing operates to isolate the vehicle from shock. The elastomeric bushing, which is located between the outer metal sleeve and the thrust bearing, effectively isolates the frame of the vehicle from the unsprung components. In certain high load applications, the ends of the outer metal sleeve are curved or bent over the ends of the inner metal sleeve in order to further encapsulate the elastomeric bushing. The curving or bending of the ends of the outer metal sleeve and thus the further encapsulating of the elastomeric bushing improves the radial spring rate, the axial spring rate, the axial retention, and the durability of the elastomeric bushing.
While these elastomer isolated bushing assemblies have performed satisfactorily in the field, noise, vibration, and harshness (NVH) problems can occur because the thrust bearing has a tendency to move longitudinally relative to the inner metal sleeve, causing free play in the bushing assembly and a clicking noise. This free play can also accelerate wear within the bushing assembly and therefore can decrease service life. Thus, there remains a need for the development of new bushing assemblies with improvements in NVH performance and durability, while minimizing the manufacturing costs associated with bushing assemblies.